(1) Field of the Invention
The present invention relates to pumping systems and more specifically to self-contained pumping systems that provide a peristaltic pumping action.
(2) Description of the Prior Art
Conventional peristaltic pumps move fluid through a tubular diaphragm by peristaltic motion, i.e. by compressing a diaphragm at successive areas along its length thereby to move the fluid through the diaphragm in front of a point of compression. A typical peristaltic pump comprises a cylindrical chamber having a tubular, flexible diaphragm disposed circumferentially, i.e. in a loop, along an inner cylindrical wall of the chamber. Two end portions of the diaphragm provide inlet and outlet ports for fluid entering and leaving the pump. A compression roller mounted within the cylindrical chamber has a diameter that is smaller than the inner diameter of the cylindrical chamber. An external driver, typically an electric motor, drives the roller in a circular path about the axis of the cylindrical wall. As the compression roller moves along this path, it compresses the diaphragm at successive positions around the periphery of the diaphragm. Fluid trapped ahead of the compression point moves in the direction of rotation of the roller and exits under positive pressure through an outlet port. During one pumping cycle, a quantity of fluid enters the inlet port, is displaced through the diaphragm loop by the progressive compressive engagement of the roller against the diaphragm and exits from the outlet port.
The following patents disclose different embodiments of conventional peristaltic pumps:
U.S. Pat. No. 664,507 (1900), Singer
U.S. Pat. No. 2,123,781 (1938), Huber
U.S. Pat. No. 2,651,264 (1953), Bruckman
U.S. Pat. No. 3,279,388 (1966), Roudaut
U.S. Pat. No. 3,597,123 (1971), Lutz
U.S. Pat. No. 4,645,434 (1987), Bogen
U.S. Pat. No. 664,507 to Singer discloses a peristaltic pump that compresses gases to liquids. The pump comprises concentric inner and outer cylindrical chambers. The outer chamber contains liquid coolant that condenses gaseous substances to liquid form as the substances are pumped through the inner chamber. A cylindrical diaphragm attaches at one position to the inner cylindrical cylinder to form a pumping volume. A compression roller mounts to a motor-driven shaft by means of a crank and is sized and positioned to compress one portion of the diaphragm and essentially divide the pumping volume into chambers. As an external motor rotates the shaft, the compression roller pump moves the compression position around the inner cylinder in a progressive fashion.
U.S. Pat. No. 2,123,781 to Huber discloses a peristaltic pump having a cylindrical housing. A series of cylindrical pins are disposed upon, and extend outwardly from, the periphery of a main oblong compression roller mounted in the center of the housing for rotation by an external motor. The oblong nature of the compression roller provides compression along a major axis. The pins provide increasing compression at successive areas along the length of the tubular diaphragm thereby to prolong the life of the diaphragm.
U.S. Pat. No. 2,651,264 to Bruckman discloses a pump having a looped tubular diaphragm and a compression roller disposed within a cylindrical housing. Like the apparatus shown in the Singer patent, an external motor drives a shaft and a crank that offsets the compression roller so that it moves on a circular path to move a compression position around the looped diaphragm.
U.S. Pat. No. 3,279,388 to Roudaut discloses a pump for corrosive liquids that comprises a cylindrical pump housing, a tubular diaphragm having magnetic rings disposed along its length, helical magnetic windings mounted on a shaft adjacent to the diaphragm, and a magnetically permeable partition between the diaphragm and rotating elements. When an external drive rotates the shaft, the rings along the length of the diaphragm are successively projected toward and away from the pump housing. This causes compression and expansion at successive positions along the length of the diaphragm. Consequently, fluid trapped between the diaphragm wall and the pump housing moves from an inlet port to an outlet port in a peristaltic fashion.
U.S. Pat. No. 3,597,123 to Lutz discloses a peristaltic pump with a cylindrical housing, a tubular flexible strip mounted within the casing and attached to the inner surface of the casing between the inlet and outlet ports, and a cylindrical compression roller rotatably mounted inside the strip. The circumference of the strip is smaller than the inner circumference of the casing. An external drive rotates a main shaft that carries a radial arm and a spring structure that supports the compression roller and biases it toward the cylindrical housing. This action forces a portion of the flexible strip against the housing to form two variable volume pumping chambers between the cylindrical housing and the flexible strip. Lutz also discloses a pump having two similar peristaltic pumps arranged side-by-side with their radial arms and rollers offset by 180.degree. to increase pumping capacity.
U.S. Pat. No. 4,645,434 to Bogen discloses a peristaltic pump having a valve arm that reciprocates to close an outlet port at the end of each pumping cycle. In this pump, a radial arm and roller drive a circumscribing ring radially outward to engage successive portions of a tubular structure contained by a cylindrical housing.
The foregoing patents disclose pumping apparatus characterized by peristaltic pumping. That is, each apparatus operates by entrapping a volume of fluid and moving it by rotation of a constriction in a diaphragm. With some fluids, such as blood, resulting shear forces associated with the moving constriction can destroy the fluid. Other forces, most notably the forces required at the constriction to prevent backflow, can limit the useful life of the diaphragm. Each of these peristaltic pumps also requires an external motor drive. Such motor drives can, in some applications, increase noise associated with pumping beyond acceptable levels. In other applications the volume or area required for the pump and drive may exceed the space available.
The following patents disclose pumps that vary the volume of a pumping chamber without introducing excessive shear forces in the pumped fluid and without requiring an external motor drive.
U.S. Pat. No. 2,875,695 (1959), Justice
U.S. Pat. No. 3,768,931 (1973), Willis
U.S. Pat. No. 2,875,695 to Justice discloses a hydraulic pump comprising a cylindrical stator for generating a rotating magnetic field and a tubular coil carrying displaceable steel balls that are interspersed throughout the fluid to be pumped. The rotating magnetic field moves the balls through the tubular coil thereby pushing fluid contained in front of each ball through the coil to an output port.
U.S. Pat. No. 3,768,391 to Willis discloses an artificial heart. A pumping chamber comprises an inner flexible bag having a plurality of evenly-spaced magnets disposed on its outer surface and unidirectional inlet and outlet ports. An outer shell circumscribes the chamber and has a plurality of electromagnets. The magnetic field generated by each electromagnet interacts with a corresponding magnet on the inner bag. When electrical current is applied in one direction, the magnetic forces repel and collapse the bag forcing fluid from the interior of the bag. When current reverses, the magnetic fields attract and expand the bag to allow fluid to fill the bag. Pumping action is achieved by alternating the direction of current flow through the electromagnets.
Each of the Justice and Willis patents discloses a pump without an external drive. However, in each the pumping mechanism is more complex than the tubular diaphragm and compression roller found in peristaltic pumps. Moreover, as magnetic air gaps in each embodiment change during use due to physical structural limitations, the magnetic fields must change accordingly to produce a constant force. If energizing level of the electromagnets is to be constant, the electromagnets and power supplies must be selected for operation at the maximum air gap, even though the fields will, on average, be greater than needed.
The following patents disclose structures that provide both motive and pumping actions
U.S. Pat. No. 1,759,766 (1930), Szmukler
U.S. Pat. No. 1,849,222 (1932), Canton
U.S. Pat. No. 2,898,032 (1959), Katzenberger
In each of these references, a cylindrical stator generates a rotating magnetic field for turning a rotor structure. The rotor structure produces a variable volume pumping volume. In U.S. Pat. No. 1,759,766 to Szmukler, a hollow, tubular shaft is held stationary. As the rotor rotates about the shaft, cell-like plungers produce a pumping action. In U.S. Pat. No. 1,849,222 to Canton, a rotor mounts on an eccentric shaft and carries circumferentially spaced, axially extending, slidable plates that form rotary seals to sweep fluid from an input port to an output port. In U.S. Pat. No. 2,898,032 to Katzenberger, a rotor turns about a stationary shaft and carries an eccentrically mounted cylinder that forms a pumping volume. A radially extendible finger supported by a stationary shaft sweeps across the surface of the cylinder as it turns with the rotor.
The following patents disclose other embodiments of variable volume pumps:
U.S. Pat. No. 2,250,947 (1941), Carpenter
U.S. Pat. No. 3,992,132 (1976), Putt
U.S. Pat. No. 4,574,644 (1986), Lew et al.
U.S. Pat. No. 2,250,947 to Carpenter discloses a guiding block that holds radially expandable pole pieces and that mounts eccentrically in a stator. U.S. Pat. No. 3,992,132 to Putt discloses an externally driven rotary magnet that passes radially extending, magnetic plungers that reciprocated in pumping chambers. U.S. Pat. No. 4,574,644 to Lew et al. discloses a variable volume pump in which an externally driven magnet moves balls around a toroidal cavity.
Each of the foregoing two groups of references discloses variable volume pumps. Some are self-contained. That is, some provide the motive and pumping functions with common rotor components. Each housing requires some complicated sealing structure. Components also slide against each other, so each is subject to generating noise. None incorporates a peristaltic pumping action with its greater simplicity. None seems readily adopted for being the basic building block of a multistage pump.